This invention relates in general to earth boring bits, an in particular to a bit of the type that utilizes air pumped through its bearings for cooling.
One type of earth boring operation utilizes air as the drilling fluid. Air is pumped down the drill string, where it exits through nozzles in the drill bit. One type of drill bit has three cutters rotatably mounted on bearing pins. As the drill string is rotated, the cutters rotate in their bearing pins to disintegrate the earth. Much of the air passing through the drill string exits through nozzles located between the cutters.
Normally, about one third of the air volume is directed through the bearings for cooling. The bearings include a set of roller bearings located near the back face of the cutter. An annular clearance exists between the bit leg and the backface for discharging air out of the bearings into the borehole. The clearance is larger on the upper side than on the lower side of the bearing pin so that most of the air vents on the upper side of the bearing pin under the bit shroud.
While these bits are successful, cuttings tend to build up around the bit and not be flushed to the surface by the air. This causes wear on the outer diameter of the bit legs of the bit.